A washing machine is an apparatus to wash laundry using electricity, and generally includes a tub to store wash water, a spin basket (rotary tub) rotatably installed in the tub, a pulsator rotatably installed on the bottom of the spin basket, and a motor and a clutch assembly to rotate the spin basket and the pulsator. The washing machine further includes an external frame to support weight of the tub and a suspension unit to interconnect the tub and the external frame.
The suspension unit connected to the washing machine is configured to reduce movement of the tub by force through which the tub moves in up, down, left, and right directions according to rotation of the pulsator and the spin basket during washing and dehydration processes. The suspension unit includes a suspension bar connected to a frame forming the external appearance of the washing machine, a spring, and a frictional damper. The suspension bar is suspended from an upper corner of the frame, and is connected to the bottom of the tub so as to support the weight of the tub. The spring for absorbing vibration is configured to attenuate vibration using frictional force based on a displacement.
A conventional suspension device includes a spring and a damper installed in a longitudinal direction of the suspension bar, such that vertical vibration and horizontal vibration can be absorbed according to the installation angles of the spring and the damper. Various kinds of suspension devices are generally used according to various use conditions and various damping schemes, for example, an silence-type suspension device, a case-shaped suspension device, a hybrid-type suspension device, etc.
After a tub is installed in the frame of the conventional suspension device, the conventional suspension device supports the weight and vibration of the tub during washing/dehydrating processes. The conventional suspension device generally absorbs and attenuates only vertical vibration by the spring and the frictional damper installed in the longitudinal direction. Attenuation weight corresponding to a horizontal vector component calculated by the installation angle of the suspension device is applied to horizontal vibration, such that vibration attenuation relatively lower than in the horizontal direction is carried out. In other words, if the suspension attachment angle is large, vertical attenuation force decreases whereas the attenuation weight increases. In contrast, if the suspension attachment angle is small, horizontal attenuation weight decreases whereas vertical attenuation weight increases.
Therefore, if the user desires to increase capacity by increasing only a tub diameter within the same frame width, the suspension attachment angle must be set to a small angle, such that horizontal attenuation force is reduced and horizontal vibration displacement caused by tub vibration is increased. As a result, the conventional suspension device unavoidably contacts the frame, and has difficulty to overcome such vibration displacement, resulting in reduction of washing ability of laundry.